1. Field of the Invention
This invention relates to a component fixing method suitably used for mounting a film condenser (film capacitor) (used in a high-voltage circuit) on a printed circuit board (PCB).
2. Description of the Related Art
FIG. 7 show a conventional adhesively-bonding method, and FIG. 8 shows a conventional mechanical fixing method. FIG. 9 shows conventional taping methods, and FIG. 9A is a cross-sectional view showing a condition in which an adhesive double coated tape is bonded to a lower surface of a film capacitor over an entire area thereof, and FIG. 9B is a cross-sectional view showing a condition in which an adhesive double coated tape is bonded only to a lower surface of a concave portion of a film capacitor, and FIG. 9C is a cross-sectional view showing a condition in which a thin adhesive double coated tape is used.
Film capacitors of this kind must be increased in size so as to withstand a high pressure. Therefore, when mounting the film capacitor on a printed circuit board of an on-vehicle equipment or the like liable to be affected by vibrations, it is highly necessary to fix the film capacitor to the printed circuit board to thereby enhance a vibration resistance so that large stresses due to vibrations will not act on soldered portions and lead portions.
As such a film capacitor fixing method, there has heretofore been extensively used a method (i.e., adhesively-bonding method) of adhesively bonding a film capacitor 2 to a printed circuit board 1 by an adhesive 5 as shown in FIG. 7. Also, as shown in FIGS. 8A and 8B, there can be proposed a method (i.e., mechanically fixing method) of mechanically fixing a film capacitor 2 to a printed circuit board 1 by a fixing member 3. Further, as shown in FIG. 9, there has been proposed a method (i.e., taping method) of bonding the film capacitor 2 to a printed circuit board 1 by the adhesive double coated tape 6 (see, for example, Patent Literature 1).                Patent Literature 1: JP-A-4-247685        
However, these three kinds of fixing methods have respective problems still remaining unsolved as described below.
First, in the adhesively-bonding method, the influence of environment-affecting substances (such as a volatile organic compound (VOC)) contained in the adhesive 5 has developed into a social problem, and besides it is difficult to control a bonding strength because of problems with respect to the amount of coating of the adhesive, coating portions, the drying time, the handling until the drying operation, etc.
The mechanical fixing method lacks in reliability and compactness. Namely, a variation in outer size of the film capacitor 2 is large because of its producing process, and therefore it is difficult to surely fix the film capacitor. Incidentally, in the case where the film capacitor 2 is of the encased type, that is, is housed in a case, a variation in outer size is small, but there is encountered a drawback that the overall size of the film capacitor 2 increases because of the provision of the case. In addition, stresses on the soldered portions and the printed circuit board 1 are increased by the fixing operation using the fixing member 3. Furthermore, the overall size in a mounted condition of the film capacity increases because of the use of the fixing member 3.
In the taping method, various disadvantages described below are encountered even when the adhesive double coated tape 6 is bonded to any portion of the lower surface of the film capacitor 2. The taping method lacks in economy and reliability.
Namely, when the adhesive double coated tape 6 is bonded to the lower surface of the film capacitor over the entire area thereof as shown in FIG. 9A, the actual bonding areas are limited to electrode portions 2a although the area of the adhesive double coated tape 6 is large. As a result, there is encountered an irrational situation in which although the material cost for the adhesive double coated tape 6 increases because of an increased amount of the used adhesive double coated tape 6, the bonding strength is lowered because of the reduced bonding area. In addition, the mounting height is certainly increased by an amount corresponding to the thickness of the adhesive double coated tape 6, and therefore the film capacitor is liable to resonate, and stresses develop at the soldered portions and legs (lead wires) of the film capacitor. Even when the adhesive double coated tape 6 is bonded only to the electrode portions 2a of the film capacitor 2, the problems with respect to the lowered bonding strength, the resonance and the stresses can not be solved.
On the other hand, in order that the adhesive double coated tape 6 can be bonded only to the lower surface of the concave portion 2b of the film capacitor 2 as shown in FIG. 9B, the adhesive double coated tape 6 need to have a thickness larger than a concave-convex height difference L1. As a result, the mounting height is certainly increased by an amount corresponding to the difference between the thickness of the adhesive double coated tape 6 and the concave-convex height difference L1. In addition, since the adhesive double coated tape 6 has the increased thickness, the material cost for the adhesive double coated tape 6 increases, and also the risk of increasing the amount of environment-affecting substances becomes high. However, if the adhesive double coated tape 6 is decreased in thickness, there is a fear that the concave-convex height difference L1 of the film capacitor 2 can not be absorbed, thus resulting in defective adhesive bonding, as shown in FIG. 9C.